In the case of tungsten-inert gas welding TIG or in the case of metal-inert gas welding (MIG), various factors impose far greater limitations on the choice of the shielding gas than is the case, for example, with metal-active gas welding (MAG). Thus, with MAG welding, active components such as oxygen and carbon dioxide are frequently added to the basic gas, argon, which is often used in this type of welding. THis gives rise to substantial improvements in the welding process as well as in the welding results in comparison to welding with a pure inert gas, that is to say, with argon, helium or argon-helium mixtures.
The limitations are particularly pronounced with respect to the addition of other components to the inert gas used for aluminum welding. Here, disruptive effects occur immediately due to the high level of reactivity of the aluminum. Thus, for instance, hydrogen causes the formation of pores, while oxygen and nitrogen form oxides or nitrides. Just in terms of the appearance of the welding seam, this is not acceptable. For this reason, when aluminum is being welded, technically pure inert gases, that is, argon or argon-helium mixtures with a degree of purity of at least 99.996% are used. Consequently, the sum of all of the impurities amounts to a maximum of 40 ppm.